C. Wayne Smith

After corneal epithelial abrasion, leukocytes and platelets rapidly enter the corneal stroma, and CCR6+ IL‐17+ γδ T cells migrate into the epithelium. γδ T‐cell‐deficient (TCRδ ^–/– ) mice have significantly reduced inflammation and epithelial wound healing. Epithelial CCL20 mRNA increased 19‐fold at 3 h, and protein increased ~ 16‐fold at 6 h after injury. Systemic or topical treatment of wild‐type C57BL/6 mice with anti‐CCL20 reduced γδ T‐cell accumulation in the cornea by >50% with a concomitant decrease in epithelial healing and stromal inflammation. In addition to CCR6 and IL‐17, corneal γδ T cells stained positively for RORγt, IL‐23R, and IL‐22. Anti‐IL‐22 reduced peak cell division of the healing epithelium by 52%. Treatment of TCRδ ^–/– mice with rIL‐22 significantly promoted wound closure, with peak epithelial cell division increased > 3‐fold. In addition, rIL‐22 restored neutrophil and platelet influx in the TCRδ ^–/– mice to wild‐type levels and increased CXCL1 production by wounded corneal explants > 2‐fold. These results indicate that an important aspect of the healing response to corneal epithelial abrasion includes CCL20‐dependent influx of CCR6+ IL‐17+ IL‐22+ γδ T cells and that IL‐22 contributes to the inflammatory response and promotes epithelial healing.—Li, Z., Burns, A. R., Byeseda Miller, S., Smith, C. W. CCL20, γδ T cells, and IL‐22 in corneal epithelial healing. FASEB J. 25, 2659–2668 (2011). www.fasebj.org

Diets high in cholesterol and cholate such as the Paigen diet have been used to study atherogenesis, lithogenesis, and proinflammatory microvascular changes induced by nutritional hypercholesterolemia. Although these diets lead to chronic hepatic inflammation and fibrosis, the early inflammatory changes have been poorly characterized. TLR4, a known receptor for LPS, is also a receptor for a variety of endogenous ligands and has been implicated in atheroma formation. Here, we specifically examined the early inflammatory response of the liver to the atherogenic (ATH) diet and the possible contribution of TLR4. Animals fed the high-cholesterol/cholate diet for 3 weeks developed a significant, predominantly mononuclear leukocyte infiltration in the liver, hepatic steatosis, elevated hepatic expression of MCP-1, RANTES, and MIP-2, and increased serum levels of liver enzymes. In TLR4-deleted animals, there was a 30% attenuation in the serum alanine transaminase levels and a 50% reduction in the leukocyte infiltration with a fourfold reduction in chemokine expression. In contrast, hepatic steatosis did not differ from wild-type controls. TLR2 deletion had no effect on diet-induced hepatitis but increased the amount of steatosis. We conclude that the early inflammatory liver injury but not hepatic lipid loading induced by the ATH diet in mice is mediated in part by TLR4.

In this issue of the Journal, Erridge et al (1) cited work from several laboratories on postprandial activation of blood leukocytes. The evidence of leukocyte activation in these studies includes increases in circulating leukocytes (neutrophils, lymphocytes, and platelets), activation of the transcription factor nuclear transcription factor κB (NF-κB) in peripheral blood mononuclear cells, increased expression of tumor necrosis factor-α (TNF-α) in monocytes, and alterations in some surface adhesion molecules in neutrophils and monocytes (eg, increased surface levels of CD11B, the α-subunit of one member of the β₂ integrin family). The test diets that apparently induced these changes were high in fat (eg, butter or cream), glucose, or mixed carbohydrates and fats. The mechanisms for this acute postprandial activation of inflammation are unclear. Ting et al (2) recently reported that triacylglycerol-rich lipoproteins isolated from 3.5 h postprandial blood significantly augmented TNF-α–dependent activation of endothelial cells, which resulted in the expression of adhesion molecules capable of capturing monocytes under conditions of fluid shear. Erridge et al provide evidence of postprandial elevations in venous blood samples of endotoxin (lipopolysaccharide), a cell wall component derived primarily from Gram-negative bacteria. Published evidence (cited by Erridge et al) from animal models and human investigations is consistent with endotoxin release from the gut. Given the fact that leukocytes, particularly monocytes, and endothelial cells express the Toll-like receptor 4 (TLR4) complex, a key cell surface–signaling receptor for endotoxin, postprandial elevations in blood endotoxin may contribute to leukocyte and endothelial activation. Shi et al (3) raise additional considerations. They showed that the saturated free fatty acids (FFAs) lauric acid (12:0), myristic acid (14:0), palmitic acid (16:0), and stearic acid (18:0) stimulate macrophage activation of NF-κB and expression of proinflammatory cytokines. These responses were largely dependent on the TLR4 receptor complex. Thus, postprandial activation of inflammation appears multifactorial, possibly involving several potential agonists for the TLR4 receptor complex as well as other mechanisms.

Objective: To determine whether the leukocyte adhesion receptors ICAM‐1 and Mac‐1, regulators of immune cell migration, have an intrinsic role within adipose tissue by 1) analyzing the expression of ICAM‐1 in adipose tissue, 2) identifying leukocyte populations within adipose tissue, and 3) determining whether ICAM‐1 and Mac‐1 mutant mice exhibit abnormal numbers of adipose tissue leukocytes.Research Methods and Procedures: Wild‐type, ICAM‐1^−/−, and Mac‐1^−/− mice were fed a long‐term high‐fat diet. ICAM‐1 expression was analyzed by Northern blot and immunohistochemistry. Leukocytes within adipose tissue were identified by immunohistochemistry and flow cytometry.Results: ICAM‐1 was expressed in adipose tissue and localized to the vascular endothelium. Macrophages and lymphocytes were prevalent within the stromal‐vascular cell fraction of adipose tissue, and gender‐specific differences were observed, with adipose tissue from female mice containing significantly more macrophages than tissue from male mice. Numbers of leukocytes in ICAM‐1^−/− and Mac‐1^−/− mice were not different from wild‐types, however, indicating that these adhesion receptors are not required for leukocyte migration into adipose tissue.Discussion: Our results documented leukocyte populations within adipose tissue, which may be involved in the development of heightened inflammation that is characteristic of obesity.